Modern wireless networks are heterogeneous in nature where different Radio Access Technologies (RATs) co-exist in the same coverage area. The co-existence of different RATs requires improved Radio Resource Management (RRM) to support the provision of pre-defined Quality of Service (QoS) and efficient utilization of radio resources. The RRM can dynamically manage the allocation and de-allocation of radio resources between different RATs, allowing seamless transition from one RAT to another when a wireless device is enabled for multi-mode operation.
FIG. 1 illustrates an exemplary network configuration 10 showing a heterogeneous wireless network 11 containing two different Radio Access Networks (RANs) 12, 14, wherein each RAN supports a corresponding different RAT. The network 11 may be a cellular telephone network operated, managed, owned, or leased by a wireless/cellular service provider (or operator). As can be seen from FIG. 1, two different RATs 12, 14 may co-exist within the same operator network or geographical coverage area. Each RAT may be supported by its corresponding RAN, which provides radio interface to a wireless device 16 to enable the device 16 to communicate with various entities (not shown) in the operator network 11 (and beyond) using a device-selected RAT. In FIG. 1, such radio interface is symbolically depicted by the exemplary wireless links 18 and 19. The operator network 11 may be coupled to a centralized RRM unit 20 via an Internet Protocol (IP) network (such as, for example, the Internet) 22. The RRM unit 20 may dynamically manage the allocation and de-allocation of radio resources between different RATs 12, 14. As mentioned before, in a heterogeneous network, different RATs co-exist in the same coverage area. Thus, instead of performing the management of radio resources independently for each RAT, the network operator may opt for an RRM 20 to provide a centralized form of overall and global management of the pool of radio resources to support the provision of QoS for wireless devices and efficient utilization of radio resources. The RRM unit 20 may be part of a group of operator-specific software modules (or applications) residing in and accessible through the IP network 22. Although not shown in FIG. 1, the RANs 12, 14 may be coupled to a Core Network (CN) portion of the operator's network 11. In one embodiment, a common CN functionality may be shared between the two RANs 12, 14. Alternatively, each RAN 12, 14 may have its own associated CN, and some form of interworking may be employed to link the two RAN-specific core networks.
In case of cellular access, the term “Access Network” (AN) may include not only a RAN portion (comprising, for example, a base station with or without a base station controller) of a cellular carrier network (e.g., the network 11), but other portions such as a cellular backhaul and core network as well. A cellular RAN such as the RANs 12, 14 may include multiple cell sites (not shown), each under the radio coverage of a respective Base Station (BS) or Base Transceiver Station (BTS) (not shown). The base stations may be, for example, evolved NodeBs (eNodeBs or eNBs), high power and macro-cell base stations or relay nodes, etc. These base stations may receive wireless communication (as indicated by exemplary radio links 18-19) from the wireless terminal 16 (and other such terminals operating in the network 11), and forward the received communication to a respective Core Network (CN). The wireless terminals may use suitable RATs (examples of which are given later below) to communicate with the base stations in the RAN. In case of a Third Generation (3G) RAN, for example, the cellular backhaul (not shown) may include functionalities of a 3G Radio Network Controller (RNC) or Base Station Controller (BSC). Portions of the backhaul (such as, for example, BSC's or RNC's) together with base stations may be considered to comprise the RAN portion of the network. The Core Network (CN), on the other hand, may provide logical, service, and control functions (e.g., subscriber account management, billing, subscriber mobility management, etc.), Internet Protocol (IP) connectivity and interconnection to other networks (e.g., the Internet or the Internet-based service network 22) or entities, roaming support, etc. The CN may be, for example, an International Mobile Telecommunications (IMT) CN such as a Third Generation Partnership Project (3GPP) CN or a 3GPP2 CN (for Code Division Multiple Access (CDMA) based cellular systems), or an ETSI TISPAN (European Telecommunications Standards Institute TIPHON (Telecommunications and Internet Protocol Harmonization over Networks) and SPAN (Services and Protocols for Advanced Networks)) CN.
From the above, it is observed that the term “RAT” signifies a specific radio access technology used by the wireless device 16 while communicating with a given “RAN.” Whereas, the term “RAN” refers to a portion (including hardware and software modules) of the service provider's AN that facilitates voice calls, data transfers, and multimedia applications (e.g., Internet access, online gaming, content downloads, video chat, etc.) for the wireless device 16. Despite such clear technical distinctions between a “RAN” and a “RAT,” these two terms still remain technically closely-linked or intertwined. Therefore, these terms may be used interchangeably herein for ease of discussion. Thus, for example, a sentence like “The wireless device is operating in the secondary RAT” is in fact a shorthand version of the technically more accurate sentence: “The wireless device is operating in the secondary RAN (and communicating with that RAN using the secondary RAT).” The interchangeable use of the terms “RAN” and “RAT” may slightly sacrifice such technical accuracy, but the desired meaning is suitably conveyed through the context of discussion. However, if the context of discussion below requires more clarity, the term “RAN” may be specifically used instead of “RAT.” It is also understood that although a RAN may support more than one RAT, for ease of discussion below, it may be assumed that each RAN 12, 14 supports only one corresponding RAT. However, the applicability of the teachings of the present disclosure is not limited to such one-to-one correspondence between a RAN and a RAT.
Some exemplary RANs include RANs in Third Generation Partnership Project's (3GPP) Global System for Mobile communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and LTE Advanced (LTE-A) networks. These RANS include, for example, GERAN (GSM/EDGE RAN, where “EDGE” refers to Enhanced Data Rate for GSM Evolution systems), Universal Terrestrial Radio Access Network (UTRAN), and Evolved-UTRAN (E-UTRAN). The corresponding RATs for these 3GPP networks are: GSM/EDGE for GERAN, UTRA for UTRAN, E-UTRA for E-UTRAN, and Wideband Code Division Multiple Access (WCDMA) based High Speed Packet Access (HSPA) for UTRAN or E-UTRAN. Similarly, Evolution-Data Optimized (EV-DO) based evolved Access Network (eAN) is an exemplary RAN in 3GPP2's Code Division Multiple Access (CDMA) based systems, and its corresponding RATs are 3GPP2's CDMA based High Rate Packet Data (HRPD) or evolved HRPD (eHRPD) technologies. As another example, HRPD technology or Wireless Local Area Network (WLAN) technology may be used as RATs for a Worldwide Interoperability for Microwave Access (WiMAX) RAN based on Institute of Electrical and Electronics Engineers (IEEE) standards such as, for example, IEEE 802.16e and 802.16m.
In case of a 3GPP network such as an LTE network, the wireless device 16 may be a User Equipment (UE) or a Mobile Station (MS). In case of an HRPD network, the wireless device 16 may be an Access Terminal (AT) (or evolved AT). Generally, the wireless device 16 (also referred to by various analogous terms such as “mobile handset,” “wireless handset,” “terminal,” etc.) may be any multi-mode mobile handset enabled (e.g., by the device manufacturer or the network operator) for communications over the primary and the secondary RATs. Some examples of such mobile handsets/devices include cellular telephones or data transfer equipments (e.g., a Personal Digital Assistant (PDA) or a pager), smartphones (e.g., iPhone™, Android™ phones, Blackberry™, etc.), handheld or laptop computers, Bluetooth® devices, electronic readers, portable electronic tablets, etc. For the sake of simplicity, in the discussion herein, the term “UE” may be primarily used as representative of all such wireless devices (i.e., AT's, MS's, or other mobile terminals), regardless of the type (i.e., whether a 3GPP system, a 3GPP2 system, etc.) of the primary and secondary RANs/RATs.
For ease of discussion of inter-RAT load balancing, one RAT is considered as a “primary” RAT whereas the other RAT is considered as a “secondary” RAT. Thus, for example, in FIG. 1, the primary RAT is identified by reference numeral “12” whereas the secondary RAT is identified by reference numeral “14.” It is noted here that the “primary” and “secondary” designations do not imply that the secondary RAT is somehow inferior to or less preferred than the primary RAT. Rather, the term “primary” is generally used to refer to a RAT that a wireless device (e.g., the device 16 in FIG. 1) is programmed (or provisioned) (e.g., by the operator of the network 11) to camp on (in an idle state) or switch to (in an active state) whenever the device receives wireless communication from that RAT. Thus, for example, when the wireless device 16 is in the coverage area of the secondary RAT 14 (and receives wireless communication from the secondary RAT 14), but also receives signals from the primary RAT 12, the wireless device 16 may attempt to camp on the primary RAT 12 when the device is in an idle state (i.e., no traffic channel established over the secondary RAT 14) or may attempt to switch to the primary RAT 12 when the wireless device is in an active state (i.e., a traffic channel established over the secondary RAT 14). In other words, a “primary” RAT may be considered as a RAT that a wireless device prefers to use first if it has a choice.
As an example, the “primary” RAN/RAT 12 may be LTE E-UTRAN, whereas its corresponding “secondary” RAN/RAT 14 may be EV-DO based eAN, and vice versa. Although not shown in FIG. 1, in certain cases, geographical coverage areas of the two RANs/RATs may partially or significantly overlap. In some implementations, the primary RAN/RAT may be entirely within the geographical area covered by the secondary RAN/RAT, and vice versa. For example, in a city-wide network, LTE may be chosen for urban coverage, whereas the entire network itself may be an EV-DO network. Thus, in the urban portion, the LTE network may be entirely within the larger EV-DO network. Many other such combinations of primary and secondary RANs/RATs may be envisaged. Thus, although primary and secondary RANs/RATs 12, 14 are shown in a non-overlapping configuration in FIG. 1, it is understood that the teachings of the present disclosure apply to other configurations of these RATs as well (e.g., full overlap, partial overlap, etc.).
As mentioned earlier, in many implementations, the UEs select to camp on their primary RAT whenever possible. This may create load imbalance if the system has primary and secondary RATs “overlaid” (e.g., when the primary RAT's geographical coverage area is entirely within the secondary RAT's geographical coverage area). Also, in some situations, the primary RAT may be congested, but the overlaid secondary RAT is lightly loaded. The UE may be in the idle state and continue to try to reselect to the primary RAT even when entering the overlaid geographic area (i.e., the area covered by the secondary RAT). This situation may further worsen the congestion issue on the primary RAT.
At present, there are two proposed solutions to address the inter-RAT load imbalance issue mentioned above.
In the first solution, all UEs belonging to the network operator are pre-provisioned into different groups. For example, the operator may have eight groups for all the subscribed UEs. During the initial activation (e.g., activation of a new subscriber account, or the very first time a UE is turned on in the operator network), the operator may assign a group number to a UE, and the group number may be stored in a secure memory location (e.g., in a UE's Subscriber Identity Module (SIM) card). How the operator assigns (or pre-provisions) a group number to each individual subscribing UE is operator dependent. However, in general, the operator may try to evenly distribute the subscribing UEs over all of the pre-defined groups. For example, in case of 1000 UEs and ten (10) groups, each group may be assigned 100 UEs. One way to assign a UE to a group is to assign a group number to the UE based on the last digit of UE's International Mobile Subscriber Identity (IMSI) number.
When the secondary RAN/RAT receives information from the primary RAN/RAT that the primary RAT is getting overloaded, the secondary RAT may broadcast a message (through secondary RAN) to all UEs operating under the secondary RAT. The broadcast message may assign the number “1” to certain groups of UEs and number “0” to the remaining groups of UEs. This enables only those UEs whose groups are assigned the number “1” to camp on the primary RAT. Thus, only the UEs belonging to these “enabled” groups are allowed to reselect the primary RAT (when the UEs are in the idle state) or switch to the primary RAT (when the UEs are in the active state). The UEs belonging to the groups having been assigned the number “0” are not allowed to idle re-select to or switch to the primary RAT, and will remain at secondary RAT.
It is noted here that the terms like “idle reselect” or “idle reselection” or other terms of similar import may be used in the discussion herein to refer to reselection of the primary RAT (as opposed to the continued selection of the current secondary RAT) by a UE that is in an idle state (in the secondary RAT).
This first solution addresses a multi-carrier configuration as well. In the multi-carrier case, each carrier belonging to the primary RAT may be listed in the broadcast message with a carrier-specific probability value. The UE in the enabled group will select a carrier based on the carrier-specific probability value, and also based on any priority value assigned to that carrier.
In the second solution, on the other hand, each UE operating under the secondary RAT (whether in the idle state or the active state) is assigned a priority value by the secondary RAT. The priority value may be assigned, for example, during an initial session establishment or even may be pre-provisioned in the UE (e.g., by the network operator upon initial activation of a subscriber account). When the secondary RAT receives information from the primary RAT that the primary RAT is getting overloaded, the secondary RAT may broadcast a message with a priority threshold. Only UEs with priority values equal to or greater than the priority threshold may be allowed to reselect the primary RAT in their idle state. Furthermore, a probability value may be broadcast along with the priority threshold for a second level of screening of UEs. If this probability value is provided, then the UEs that are eligible to camp on the primary RAT will generate a random value. Only UEs that generate the random value equal to or greater than the broadcasted probability value can eventually idle re-select to the primary RAT.